Without Ventrilo running, or running but not connected, the actual throughput fluctuates by a couple of megabits each way. When Ventrilo is running the result is always -exactly- the same.

The issue is system-wide, it's not limited to iperf. When copying a file to PC1 the throughput drops from 65-70MB/sec to barely 12-13MB/sec when Ventrilo is running and connected.

I've also confirmed the issue with a friend of mine, who has spent weeks thinking there was something wrong with his gigabit network. He sees the exact same issue when Ventrilo is running and connected.

I have to wonder what on earth Ventrilo is doing to the networking stack to cause an 85-90% reduction in Rx traffic.

Hopefully someone from flagship will see this and look into the matter.

I had wondered if QoS was causing the issue, but I just disabled it and it made no difference. I'm also wondering if this issue only occurs on gigabit ethernet, as the reduced speed is still above 100Mbit.

Like I said, I've encountered this here, and also with a friend, we both have gigabit LANs and both have the problem of massively reduced speed (85%+ reduction) when Ventrilo is running and connected.

I'm the friend NeoLojik mentioned as also having the same problem. I run Ventrilo 3.0.4 (64bit) on Windows Vista Ultimate 64-bit. I've performed the same tests as him, using Iperf for Windows v1.70. The destination PC is on the same switch, and is running Windows Vista Business 32bit. This is what happens when I run Iperf with Vent running:

As you can see, it's a pretty significant performance hit. Bear in mind that this is only a *one-way* performance hit, too; if I rerun the tests in the other direction, it all works fine. This implies to me that Ventrilo is somehow affecting the RX (IE Download) bandwidth of the machine it's running on...

Further information if it's needed.
- The PC running Vent has an Asus P5K Premium Black Pearl edition mobo with an onboard Realtek RTL8110SC PCI Gigabit LAN controller. The drivers are the latest I could find, and are dated 25th May 2009. The problem occured with earlier driver versions.
- The destination PC has an Asus P5Q-EM mobo, running a Realtek 8111C PCI-E Gigabit LAN controller, drivers dated 3rd July 2009. Again, updating drivers update did not affect the problem.
- Both systems are connected to a a Netgear GS605 v2 gigabit-capable switch via known-working moulded-connector Cat5e.
- Both PCs show as connecting to the network at 1.0Gbit, and are perfectly stable at that speed.
- The RX and TX on both systems will allow for ~75-80MB/sec transfers (SATA II bottlenecks permitting) in both directions under normal operations.When the problem occurs, RX is limited to 14MB/sec.

So, does anyone have any ideas what NeoLojik and I could to to narrow down or solve this? Any help would be greatfully received.

Edit: I've updated to Ventrilo 3.0.5 (64bit), with no change to the problem.